This invention relates to a system for controlling the feed speed of a movable member in numerical control equipment or the like.
In numerically controlled machining, the optimum feed speed of a movable member, for example, the workpiece table, is decided by taking into account such factors as the life of the cutter and the machining time. If the machining or feed speed is increased without considering the optimum feed speed in an effort to shorten the machining time, the cutter is subjected to an excessive load and is likely to sustain such damage as snapping or chipping. On the other hand, if the machining speed is decreased below the optimum speed in order to prolong the life of the cutter, the numerically controlled machining operation cannot be performed efficiently because of the excessive increase in machining time. In general, the optimum machining speed is determined by considering a variety of factors such as the hardness of the workpiece, the amount of the workpiece which is to be removed by cutting, the sharpness and flexibility of the cutter and the rigidity of the machine. However, once the optimum machining speed has been determined and punched in the command tape and the machine actually placed in operation, it is often found that the machine should be run at a speed slightly lower than the optimum speed to preclude cutter damage, or at a slightly higher speed to reduce machining time. Hence it is required that a manual adjustment be made to the feed speed of the movable member, which is actually being operated by the command type, to adjust the feed speed to the true optimum feed speed.
With the conventional feed speed control system of the type described, however, the manual adjustment of the speed is carried out by manipulating a number of speed command dials, the dials in turn operating in association with corresponding oscillators. The plurality of dials and oscillators which are necessary in the prior art represent a large number of component parts and, since the space required to mount them is limited, it is difficult to construct the apparatus inexpensively and compactly. Moreover, the existence of a plurality of dials makes manual adjustment a complicated matter so that the operator must exercise caution in manipulating the dials.
Accordingly, there is a demand for a feed speed control system which does not require a large number of dials and the associated peripheral equipment.